1. Field of the Invention
This invention relates to the production of printing plates from photopolymerizable resins. More particularly, this invention relates to the production of printing plates wherein a resin layer is selectively cross-linked by being moved past a varying intensity light source.
2. Brief Description of the Art
The production of printing plates by selectively cross-linking polymerizable resins is known in the prior art. The printing plate is conventionally formed by first placing a negative on a supporting glass plate. An optically transparent release film is then placed on top of the negative which is subsequently coated with a layer of photopolymerizable resin. A backing sheet is then placed on top of the photopolymerizable resin, and the backing sheet is then covered by another glass sheet. Irradiation by actinic light, such as UV light, through the top glass/backing sheet combination forms a solid floor layer of photoresin, which adheres to the backing sheet. The thickness of the floor layer is less than the total thickness of the photoresin. Irradiation through the lower glass plate negative release sheet selectively hardens the photoresin to form an image-printing surface which mirrors the image on the negative. The hardened regions adhere to the floor layer, but not the transparent release sheet. Subsequent processing removes unhardened (liquid) photoresin to reveal a relief image.
When following the teachings of the prior art, the photopolymerizable resin layer can be placed on the glass plate and a capping blade can be drawn across the resin layer so as to level the layer of resin on the glass plate. The result is a relatively constant thickness resin layer formed on the supporting glass plate in the printing plate production assembly. The uniform layer of resin is then exposed to a UV light source through the negative so as to produce cross-linked solid areas in the resin layer which form a printing image or pattern in the resin layer. The non-cross-linked liquid portions of the resin layer are then removed from the plate, and the result is a selectively relieved cross-linked resin printing pattern on the plate. The aforesaid procedure for producing printing plates is relatively time consuming, and, is to some degree, size-restrictive. Direct production of large relief images requires large pieces of very flat glass. The photo negatives required can be both costly and time-consuming to produce.
It would be desirable to provide a process and assembly which would be able to produce different sized printing plates in a continuous fashion with, or without, the need for an image-producing negative, and without the required set up time of the prior art procedure. This is especially true for time-critical applications such as newspapers.